1. Field of the Invention
The present invention relates to a clutch unit for selectively transmitting driving force to a camera film feeder.
2. Description of the Related Art
Conventional clutch units for selectively transmitting driving force are unidirectional. Torque exerted to rotate a driving shaft in one direction is transmitted to a driven shaft, however no torque is exerted to produce rotation in an opposite direction.
A one-way clutch unit adapted for film feeding in a camera is disclosed in U.S. Pat. No. 5,136,314 and shown in FIG. 12.
In the film feeding mechanism, driving force from a drive motor 103 is transmitted to a sun gear 106 of an epicyclic gear mechanism via a pinion 104 and gear train 105. An epicyclic gear 107 meshes with a driven gear 108 or a driven gear 109.
The driven gear 108 is coupled to a gear 102a of a spool shaft 102 via a spool gear train 111. The driven gear 108 meshes with an input gear 110a of a one-way clutch 110. An output gear 110b of the one-way clutch 110 is coupled with a cartridge driving gear 113 via a cartridge gear train 112. The cartridge driving gear 113 has a fork portion 113a received in a cartridge shaft 114. As discussed throughout, direction D13 shall be a direction of normal rotation in which the one-way clutch 110 rotates normally to drive.
When the film feeding mechanism is used to feed a film 120, the driven gear 108 is rotated in a direction D11 via the epicyclic gear mechanism. The cartridge driving gear 113 is rotated via the one-way clutch 110 and gear train 112. Consequently, the film 120 is advanced. At the same time, the spool shaft 102 is driven via the spool gear train 111. After the film 120 is advanced, when the film is wound by rotating the spool shaft 102, the film is maintained in tension. An advancing rate at which a film is advanced from the spool shaft is greater than an advancing rate at which the film is advanced from the cartridge. Therefore, the cartridge driving gear 113 is rotated quickly. The output gear 110b of the one-way clutch 110 is driven in the direction D13 relatively faster than the input gear 110a. This state shall be referred to as an overrunning state. For photography, film is wound in this manner, that is, with the spool shaft driven faster.
To rewind film, the motor 103 is rotated reversely in order to cause the epicyclic gear 107 to mesh with the gear 109. The driven gear 109 is rotated in a direction D12 via the epicyclic gear mechanism. The output gear 110b of the one-way clutch 110 is driven to rotate in a direction opposite to direction D13. The cartridge driving gear 113 is driven in an opposite direction via the gear train 112. The film 120 is rewound about the cartridge shaft. The spool shaft 102 is rotated in a direction opposite to a direction of arrow F in FIG. 12 of the film 120.
The film feeding mechanism for a camera disclosed in the U.S. Pat. No. 5,136,314 employs the one-way clutch 110 for driving the spool shaft and cartridge shaft with the spool shaft interlocked with the cartridge shaft. However, the input driving gear of the one-way clutch 110 cannot drive for rotation in both directions. For rewinding the film 120, the output gear 110b must be driven directly as shown in FIG. 12. For a driving system capable of driving in both the directions, another driving system for directly driving the output gear 110b must be added. Moreover, since the one-way clutch 110 must be interposed between the cartridge driving system and spool driving system, it requires significant sufficient space for the components and leads to a complex mechanism.
Moreover, a film feeding and driving system including the one-way clutch 110 must be positioned as a unit on the bottom or top of a camera body, resulting in ineffective use of a large space for the film feeding and driving system in the camera body.